MITRA Forum Question Details

I would not contradict those at Golden as they tend to do substantial experimentation before making claims about performance. What they state is certainly true, it is important to follow those steps to create a panel that is less likely to develop cracks or checks. I would add though, in my experience and years of examining paintings and student works, it is extremely common to see some degree of checking in grounds (acrylic dispersion and glue based) on ply panels (when there is no interlayer of fabric or film). Plywood is made by basically shaving wood off of the trunk of a tree to produce a very long continuous sheet (sort of like a roll of toilet paper). This sheet is cut, flattened, and adhered, to another sheet, usually at a 90-degree angle. This creates a panel that is far less likely to warp but this flattening does introduce stresses that tend to reappear as checking along the grain. A well-sealed ply panel with a substantial acrylic dispersion ground layer may not develop these defects. Additionally acrylic dispersion grounds are far more flexible than glue grounds and would likely show less checking than glue-based grounds.

However, even for acrylic dispersion grounds, I tend to recommend gluing a fine fabric to the sized panel, applying an additional layer of size on top of the fabric after it has dried, and put the acrylic dispersion ground on the fabric layer. This resembles the methods used by the Early Italian tempera painters to diminish cracking in their true gesso grounds on panel. Others may have a different take on this.

Thanks Brian, but this happens to actually be a case where questioning us might be in order! I feel I can share that we are actively looking at changing our stance on plywood, or at least modifying it, and are just now plotting to do some testing and more thorough research. And, while the referenced article was published in Just Paint, our newsletter, the research and views were from Elaine Salazar, of Ampersand, who certainly has a long relationship to these issues and materials, thus we would continue to give them some consideration and weight. That said a few things have started to chip away at our own confidence in plywood. One, is having some cases come to us with cracking in the ground and paint layers that seemed clearly associated with the veneer used on the underlying ply. Second, a comment from an conservation scientist we were corresponding with caught our attention when they stated they felt that plywood was unsuitable for permanent works of art, and finally - while we rarely give Wet Canvas posts a lot of weight as a reference - this following one felt exceptionally well researched in terms of citing conservation research and studies from the Forrest Products Laboratory, and the points made are in line with your own comments above: 

http://www.wetcanvas.com/forums/showpost.php?p=20442188&postcount=6

So, all of that combined definitely has us taking a renewed look at alternatives, such as other types of composite, engineered wood supports, and of course aluminum composite panels remain seemingly ideal. We should also mention that internally we rely on MDO (medium density overlay) for our plywood supports, as do several of us in our own work. The resin impregnated paper surface does seem to solve some of the issues of grain and provides a smooth surface, but even there I think more research might be warranted, even though it appears to pass muster as an approved material for use in storage cases in museums.

Anyway, wanted to chime in on that one aspect at least.

​One more thing. While many people seem to assume that GAC 100 or acrylic gesso somehow seal the surface of a panel, they are actually really poor moisture barriers, which is precisely what you want to try to have on those exposed sides. For that we would recommend following our guidelines in the following article on Preparing Panels for a Life Outdoors

http://www.justpaint.org/preparing-panels-for-a-life-outdoors/

Although the focus is on exterior use, it would still represent a superior moisture barrier to many alternatives. You might also, for interior use, take a look at pigmented shellac primers, such as BIN. See my posting in a different MITRA thread on sealing hardboard with shellac for some references to support that option:

https://www.artcons.udel.edu/mitra/forums/question?QID=379

Okay, hope that helps.